Sunday, March 10, 2013

Soiled Again

As I mentioned in a previous post,  I filled the void in my yard with horse manure.  There was some soil where my garage used to be, but it was mostly clay and sand.  After talking with a coworker, I wondered if almost pure horse manure is a suitable substrate for growing vegetables.

As a geologist, I was forced to learn about soil and soil description, though I didn't necessarily retain that information.  Based on what I have heard from friends, the important aspects of soil are the soil structure and soil chemistry.


Soil structure is key for proper root growth, water drainage, and moisture retention.  Most gardeners will tell you never to step on the soil, as it compacts it and destroys the soil structure.  Organic material generally helps improve soil structure.  The USDA has a good help sheet for evaluating soil structure.

Different soil structures from the Colorado Master Gardener program.  The structures are arranged from left to right in order of how quickly they drain water.


One concern that a gardener might have is that their soil chemistry is not right for the type of plants growing.  Different plants like different ratios of nutrients and different soil pH.

The pH of soil is easy to determine and control.  The Garden Helper lists preferred soil pH levels for different plants.  It seems like most vegetables prefer a slightly acidic soil (pH 6-7).  The pH level in soil can be changed by adding lime (to make it more basic) or sulfur (to add acidity) and is described in detail in this "For Dummies" site.  Amazon and most hardware stores sell inexpensive soil pH testers.

To determine the current condition of your soil, you should have it tested by your local extension agent.  They usually provide results, interpretations, and recommendations for a reasonable fee.  The USU Extension office offers an excellent soil testing service, which is open to the public.  It is key to get a representative sample when taking soil samples to the extension agent.

Plants also require nutrients for survival.  Most fertilizers have the Nitrogen (N), phosphorus (P), and potassium (K) ratio printed on the bag, which is known as the NPK rating.  The USDA has a pretty cool crop nutrient tool to help determine NPK ratings.

My concern with all of the horse manure is burning my plants with excessive nutrients.  I found some information on this on eHow.  Based on what I have read, as long as the horse manure isn't fresh and has had time to compost, it shouldn't "burn" the plants.


Most of the garden books I have read recommend a process known as double digging to prepare soil for cultivation.  This process requires digging up a small section of the land (3x1x1  foot block), then loosening the soil under that block with a pitchfork, then digging up the adjacent block of soil and moving it to the the hole from the last spot you dug.  When preparing the soil below the old garage foundation, I double dug, and sifted the soil.

USU Extension has a pamphlet on soil preparation.  Organic gardening also has a good article on soil preparation.


Soil is an ecosystem, supporting a variety of organisms, including our plants.  Ensuring that the soil is vibrant with life could help with vegetable production.  Root nodules in some plants indicate a symbiotic relationship between plant roots and a bacteria (rhiazobia).  Amazingly enough, you can buy rhiazobia.

Red wrigglers significantly improve soil.  They break apart soil particles and increase void spaces. Nyworms, USDA and Colorado State also talk about the benefits of earthworms.  Amazon sells earthworms!

Nematodes can be both a pest and benefit.  Beneficial nematodes can kill all kinds of pests that lay their eggs in the soil.

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